1. Field of the Invention
The present invention generally relates to printhead assembly apparatus used in ink jet printers, and more particularly relates to a removable orifice plate and associated securing apparatus for such printhead assemblies.
2. Description of Related Art
A conventionally fabricated printhead assembly for an ink jet printer typically includes a piezoelectric ceramic body portion through which a spaced apart series of parallel ink receiving chambers or cavities extend from the front end of the body to its rear end. The open chamber ends at the rear end of the body are suitably communicated with the interior of an ink reservoir to receive ink therefrom, and an orifice plate, which is comprised of a dissimilar material such as a polymer, is secured over the open front end of the body using a generally planar layer of high strength adhesive material. A spaced series of ink discharge orifice openings are formed through the orifice plate, and are aligned with and positioned over the open front ends of the body chambers.
In such conventional printheads, the orifice plates are permanently secured to the front end of the printhead assembly by a strong adhesive. Generally, the orifice plate is secured in place by an adhesive that is applied either to the rear end surface of the orifice plate or the front end surface of the printhead body. The typical adhesives that are used to secure the orifice plate to the printhead body are "activated" or cured by subjecting the printhead assembly to high temperatures. After the adhesive has cured, the orifice plate is permanently bonded to the printhead body.
Because the orifice plate is permanently bonded to the printhead assembly, several disadvantages can arise with the use of these conventional ink jet printhead assemblies. For example, because of the differing coefficients of thermal expansion between the materials, the ink discharge orifices of the orifice plate can become misaligned with the ink receiving chambers when the printhead assembly is subjected to the high temperatures necessary to cure the adhesive properly. Since the ink discharge orifices and its features are extremely small, the dimensional tolerances on the size and location of these features are equally small. Therefore, any misalignment that may occur during the curing process can have a detrimental effect on the quality and the performance of the ink jet printhead. Thus, if a misalignment occurs during the assembly process that substantially affects the print quality, the entire printhead assembly must be disposed of because there is no effective way to easily remove the orifice plate from the printhead. If the defective printhead is inadvertently sold and used by a purchaser, the purchaser must either return the printhead to the place of purchase or throw the entire defective printhead assembly away since the orifice plate is permanently attached to the printhead body. Additionally, the conventional adhesives that may be used to attach the orifice plate to the body portion, must also act as a sealing gasket to seal the printhead assembly and prevent ink from leaking between the channels or various segregated areas of the printhead. Unfortunately, however, the strong solvent nature of most inks chemically attacks many common adhesives, thereby weakening the adhesive and causing structural failure and leakage. Again, if structural failure or leakage occurs as the result of the adhesive failure, the entire printhead assembly must be thrown away because the purchaser has no way of effectively reattaching and sealing the orifice plate to the printhead body.
In other instances, after the adhesive is applied to the body portion and during the step in which the orifice plate is positioned on the printhead body, the adhesive may seep into and plug the ink receiving chambers and the orifice holes. If these plugged printheads are inadvertently used by a purchaser, the purchaser, again, has no alternative but to either return the printhead, throw the entire printhead assembly away or endure an unacceptable print quality. Additionally, during operation of the printhead, the ink can become dry and plug several of the tiny discharge orifices in the orifice plate. When this occurs, the purchaser must either endure a poor print quality or throw the entire printhead assembly away.
In each instance just described, the way in which the problem of a defective orifice plate is remedied by the purchaser, and in many instances by the manufacturer, is to dispose of the entire printhead assembly. These end results are undesirable because they are costly and wasteful to both the manufacturer and the purchaser.
Therefore, it can readily be seen that there is a need in the art for a securing assembly that will allow the orifice plate to be easily removed and replaced in the case of defect or failure. The present invention provides an apparatus that addresses these needs.